The present invention relates to an improved process for flash-smelting sulfidic materials which contain copper and/or nickel as well as iron. It is particularly, though not exclusively, suitable for incorporating in a pyrometallurgical copper recovery process wherein smelting and converting are carried out in the same vessel.
In the course of recovering copper and/or nickel from sulfidic materials such as concentrates containing chalcopyrite, pyrrhotite, pentlandite, etc., the first pyrometallurgical step needed is smelting to oxidize iron and slag it off, thereby leaving a matte which is subsequently converted by blowing it with an oxidizing gas. Of the various smelting techniques known, one of the most attractive comprises flash-smelting with the aid of substantially pure oxygen, as described, for example, in Canadian Pat. No. 503,446. Such a technique which involves injection of the particulate sulfide with a stream of oxygen into the interior of a furnace chamber, where the sulfide `burns` autogenously while in a state of suspension, has the obvious attraction of fuel economy. Furthermore, the use of pure oxygen leads to offgases which are concentrated in sulfur dioxide so that the latter can be removed economically, for example, by liquefaction. Such a flash-smelting procedure has in fact been used commercially for some time by the present Assignee in its operations at Sudbury, Ontario, Canada. After the flash-smelting, the matte is converted in either a side-blown (Pierce-Smith) or a top blown vessel with the aid of oxygen or oxygen-enriched air. The furnace used currently for the flash-smelting is externally about 24 meters long, 7 meters wide and 5.5 meters high at the top of its arched roof. As a result, the process is suited only to production on a large scale, such as the treatment of one or two thousands of tonnes of concentrate daily. In the case of production on a more modest scale, the large capacity of a flash-smelter is inappropriate, and the need for separate smelting and converting vessels can make the capital costs prohibitively high. Ideally it is desirable, for small scale production, to perform both operations in a single vessel.
Various approaches have been suggested for enabling smelting to take place in a converter. These approaches can be divided into those involving batch processing and those involving continuous processing. The former category includes schemes wherein concentrate to be smelted is fed into a converter, either alone or in admixture with some matte to be converted, the converter having a starting bath of molten matte already present therein. This need for a starting bath is a distinct inconvenience inasmuch as it necessitates either a prior melting operation in a separate vessel, or a melt-down cycle in the converter vessel which is inherently an inefficient procedure. While the alternative resort to continuous or semi-continuous operation minimizes the inconvenience of the start-up bath, it no longer permits operation with a single vessel; instead it involves using two converter vessels in series.
The need for a start-up bath of molten matte does not arise when flash-smelting is resorted to since the oxidative `burning` reaction takes place not within the molten bath but rather in the furnace space above the matte, in what may be termed the `flame-zone`. It would therefore be highly desirable to be able to carry out flash-smelting in a vessel such as a Pierce-Smith converter and thereafter convert in the same vessel. The reason why such an approach has never been attempted stems from a universal belief that the flame-zone at the end of a flash-smelting gun could never be accommodated in such a confined space. Hence directing a flash-smelting gun into a converter vessel would be expected to cause a flame-zone which would impinge on the refractory of the vessel and cause refractory burn-out in a very short time. Moreover, the effect of such impingement coupled with the rapid injection of large quantities of gas and solids would be expected to lead to unacceptable dust-creation.
We have found, however, that by suitable modification to the burner and its method of operation flash-smelting can be made to take place within a much smaller and well defined flame-zone, small enough to be accommodated in a typical converter vessel.